We propose experiments to determine the roles of the peptides cholecysto kinin (CCK) and bombesin (BBS) in the physiological regulation of satiety in feeding behavior. (1) Using a variety of gastrointestinal nerve sections, we will attempt to localize the sites of action of exogenous CCK and BBS when they are administered peripherally. (2) Using a denervated gastric pouch preparation in the sham feeding rat and radioimmunoassay, we will attempt to control and measure release of endogenous BBS. (3) Using the technique of passive immunization, we will attempt to determine whether BBS is a physiological satiety signal. (4) We will attempt to determine the satiety potency and possible synergism of peripherally-administered combinations of CCK, BBS, and other putative satiety signals. (5) We will attempt to determine the phase of satiety which is most sensitive to the actions of exogenous CCK and BBS. (6) We will attempt to determine the satiety potency of other recently discovered gut and brain peptides. (7) CCK and BBS are now know to be neuropeptides contained in brain cells. Therefore, using a combination of lesion (electrical and chemical) and cannulation techniques, we will attempt to manipulate central CCk and BBS levels and to determine the effects of these manipulations on short-term food intake.